The present invention relates to a uniform strength ophthalmic lens having a gradient refractive index changing rotational-symmetrically about the optical axis.
Ophthalmic lenses having a gradient refractive index have been discussed numerous times in scientific papers. By way of illustration, we refer to the survey "GRADIENT INDEX OPTICS" by W. N. Charman (The Ophthalmic Optician, 1981, pp. 72-84) and the bibliography listed therein.
As can be learned from said article (p.80, left column), ophthalmic lenses with a gradient refraction index have hitherto been considered a substitute for ophthalmic lenses with aspheric surfaces with "comparably good" optical properties (p. 80, left column following).
A uniform strength ophthalmic lens is also known from DE-OS No. 27 07 601. From said publication it can be learned that a "careful selection of the aspheric base curve and of the refractive index gradients" can reduce aberrations more than it would be possible by means of only an aspheric base curve. To accomplish this, the refractive index is changed radially, in particular, in steps. A continuous changing of the refraction index is only mentioned in passing without presenting a definite technical method.
The problem of reducing critical thicknesses of lenses, i.e. the center thickness in plus a positive lenses and peripheral thickness in minus or negative lenses, is not discussed in the aforementioned article by W. N. Charman nor in DE-OS No. 27 07 601.